Not Idaho, but
That'll be the VIN - the Vehicle Identification Number is a unique code, including a serial number used by the automotive industry to identify individual motor vehicles; detailing their production date, order/sequence, model specs, option info, when, & where they were manufactured/came off the production line. Other's have outlined where they found their VIN. :thumbup:
That said, for many vehicle fleets, ie. all the vehicles owned by one owner/company &/or held or maintained at one site,
the company may assign a Unit Number that is usually a lot shorter than the VIN which is still a unique identifier for
THAT vehicle owned by
THAT company/at
THAT site.... and for those owners & their oil analysis purposes,
THAT's the number the oil analysis mob will likely want - the oil analysis mob are usually just after whatever unique identifier you (& they

) can use to make sure the analysis results don't get attributed to the wrong vehicle. :sour: . You would be perfectly entitled to tell them
YOUR Unit Identification number is
#1, cos this will be the first vehicle from
YOUR 'fleet' that you bought... or maybe that you've ever got an analysis for.

hyea: . Or if you wanted, it could be any other unique identifier that you chose which clearly lets
YOU identify that the analysis they send back belongs to
THAT specific vehicle...

. Or you could use the VIN that the vehicle manufacturer has already assigned as a unique identifier, an identifier which also encompasses a whole lot more info, like engine type & spec, including some details that may impact upon how your oil should be expected to perform.
Me, I'd just use the VIN, even if I (still)
had anything like a 'fleet'! :roflblack:
Enjoy! :cheers: